Process for improving polyamide filament lubricity

ABSTRACT

THE LUBRICITY OF POLYAMIDE FILAMENT CAN BE SUBSTANTIALLY IMPROVED WITHOUT SIGNIFICANTLY ALTERING THE APPEARANCE OF THE FILAMENTS BY DISPERSING A SMALL AMOUNT OF A MICROCRYSTALLINE WAX HAVING A REFRACTIVE INDEX GREATER THAN 1.5 AND LESS THAN 1.6 IN THE POLYAMIDE PRIOR TO ITS EXTRUSION IN FILAMENTARY FORM.

United States Patent O 3,560,421 PROCESS FOR IMPROVING POLYAMIDE FILAMENT LUBRICITY Paul R. Cox, Jr., and Lawrence W. Crovatt, Jr., Cary, N.C., assignors to Monsanto Company, St. Louis, Mo., a corporation of Delaware N Drawing. Continuation-impart of application Ser. No. 593,713, Nov. 14, 1966. This application July 28, 1969, Ser. No. 845,544

Int. Cl. C08g 51/52; D01f 1/02 US. Cl. 26028 11 Claims ABSTRACT OF THE DISCLOSURE The lubricity of polyamide filament can be substantially improved without significantly altering the appearance of the filaments by dispersing a small amount of a microcrystalline wax having a refractive index greater than 1.5 and less than 1.6 in the polyamide prior to its extrusion in filamentary form.

CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation'in-part of our copending application Ser. No. 593,713 which was filed on Nov. 14, 1966 and now abandoned.

BACKGROUND OF THE INVENTION It is known that in the manufacture of filaments from synthetic linear polyamides, the tenacity of the filaments can be greatly increased by the technique of drawing which comprises stretching the filaments to increase the molecular orientation of the polyamide. Although the drawing operation can be conducted by various methods, the most common procedure is carried out with two filament-advancing devices known as a feed roll and a draw roll. Filament stretching is achieved by running these rolls at different speeds with the amount of drawing or stretching determined by the ratio of the peripheral speeds of the two rolls. To localize the point at which the drawing occurs, a braking device is usually placed between the feed roll and the draw roll. Generally, the braking device is a pin (called the draw pin) around which the filaments are wrapped one or more times. The frictional drag exerted on moving filaments by the draw pin causes the stretching of the filaments to take place in the area of the draw pin. Particularly in those instances when there is a tendency toward non-uniform drawing, the use of such frictional drag to localize the stretching of the filaments is highly advantageous because it promotes greater drawing uniformity.

It is also known that the drawing operation can be faciliated in some cases by elevating the filament temperature during drawing. Heating of the filaments for that purpose may be carried out by inserting a hot pin, a hot plate or a hot fluid bath between the feed roll and draw roll or by using a heated feed roll. The elevated filament temperature is generally advantageous because the intermolecular forces in the polyamide are diminished by the resulting increase in molecular activity and the ratio of the force required to draw the filament to that required to break it is thereby lessened. It is common practice to employ a hot-drawing technique in the manufacture of polyamide filaments for uses in which high tensile strength is required, such as reinforcement of pneumatic tires. However, the maximum hot-drawing temperatures vary somewhat with the nature of the particular polyamide because they are limited by the softening point of the polymer.

A particularly troublesome problem encountered in.

3,560,421 Patented Feb. 2, 1971 ice drawing at either ambient or elevated temperatures is the occurrence of filament breakage during the drawing operation. The principal cause of such breakage is the build-up of excessive tension due to inter-filament friction which generally reaches a maximum as the filaments pass over the draw pin or other braking device. As a result, one or more individual filaments in the thread line may break and wrap around the draw roll or the entire thread line may break in which case production must be stopped until the continuity of the thread line is reestablished. Such filament breakage not only affects labor requirements and productivity but the product quality is also affected in an adverse manner.

It is known that excessive tensions resulting from the development of unduly high friction during drawing can be reduced by applying various antifriction agents to the filaments before they are drawn. These agents are generally applied from aqueous media which normally provide a more uniform and more easily controlled deposition of the agents on the filaments than nonaqueous media. However, antifriction agents deposited on the filamentary surfaces have the disadvantage that they are normally at least partially removed by wear or washing of the filaments. On the other hand, most conventional antifriction agents would undesirably modify the appearance of polyamide filaments in which they were incorporated because they have a refractive index significantly different from that of most polyamides (generally about 1.55) and therefore would alter the manner and degree in which light would be reflected by the filaments.

In the absence of a fully satisfactory way to overcome the aforementioned problems, a process whereby the lubricity of polyamide filaments can be substantially improved without significantly altering the appearance of the filaments is highly desirable, and it is an object of this invention to provide such a process.

SUMMARY OF THE INVENTION It has now been discovered that the lubricity of polyamide filaments can be substantially improved without significantly altering the appearance of the filaments by dispersing a small amount of a microcrystalline wax having a refractive index greater than 1.5 and less than 1.6 in the polyamide prior to its extrusion in filamentary form.

DETAILED DESCRIPTION OF THE INVENTION The polyamides with which this invention is concerned are synthetic, high molecular weight, fiber-forming polyamides of the general type characterized by the presence of recurring carbonamide groups as an integral part of the polymer chain and wherein such groups are separated by at least two carbon atoms. They are further characterized by high melting points, pronounced crystallinity and insolubility in most solvents except mineral acids, formic acid and/ or phenols. Upon hydrolysis with strong mineral acids the polymers typically revert to the reactants from which they were formed. The polyamides of this type are generally prepared by reacting (I) Substantially equimolar proportions of (a) at least one organic dicarboxylic acid containing from 4 to 20 carbon atoms, for example an alkylene or aromatic dicarboxylic acid such as succinic, glutaric, adipic, pimelic, suberic, azelaic, sebacic, dodecandioic, tetradecandioic, hexadecandioic, eicosandioic, terephthalie or isophthalic acid or a polyamide-forming derivative thereof such as an amide or lower alkyl (e.g. methyl, ethyl, propyl or bntyl) ester thereof or the corresponding acid halide (e.g. chloride) and (b) at least one organic diamine containing from 2 to 20 carbon atoms, for example an alkylene or aromatic diamine such as ethylene, tetramethylene, hexameth ylene, decamethylene, tetradecamethylene, octadecamethylene or phenylene diamine or a cycloalkane bisalkylamine such as cyclohexane bis-methylamine or a polyamide-forming derivative thereof such as the corresponding carbamate or N-formyl compound and/ or (II) At least one aminocarboxylic acid containing from 4 to 20 carbon atoms such as 4-aminobutanoic ('y-aminobutyric) acid, 6-aminohexanoic (2-aminocaproic) acid, 8 aminohexanoic acid, l-aminoundecanoic acid, 15- aminopentadecanoic acid or l9-aminononadecanoic acid or a polyamide-forming derivative thereof such as the corresponding lactam.

The reaction is conventionally carried out by heating the reactants under polycondensation conditions (normally including a temperature between 180 and 330 C. and in most cases between 200 and 295 C.) until the product has a sufiiciently high molecular weight to exhibit fiber-forming properties. The polymer generally exhibits such properties when it has an intrinsic viscosity of at least 0.4 as determined by the equation Intrinsic viscosity= C 30 in which N is the relative viscosity of a dilute solution of the polyamide in m-cresol in the same units and at the same temperature and C is the concentration in grams of polymer per 100 cubic centimeters of the solution. The reaction can be conducted at superatmospheric, atmospheric or subatmospheric pressure. It is often desirable, especially in the last stage of the reaction, to employ conditions (e.g. reduced pressure) which aid in the removal of reaction byproducts. Preferably, the reaction is carried out in the absence of oxygen, for example in an atmosphere of nitrogen. After a polyamide or copolyamide of the desired molecular weight is prepared, it may be extruded into filaments which are normally drawn, as aforesaid, to provide molecular orientation for greater tenacity. Instead of proceeding immediately to filament formation after polymerization has been completed, the polyamide can be solidified, if desired, and remelted for extrusion into filaments at a later time.

The wax that is dispersed in the polyamide in accordance with the present invention can be any microcrystalline wax having a refractive index greater than 1.5 and less than 1.6. As is Well known, such microcrystalline waxes are normally solid petroleum derivatives having a finer, less apparent crystalline structure than the ordinary paraifin waxes. The microcrystalline waxes are typically mixtures of hydrocarbons having a higher average molecular weight than the ordinary paraffin Waxes and usually containing at least about 40 and generally from 40 to 60 carbon atoms per average molecule. Examples of commercially available microcrystalline waxes that are highly suitable for use in the process of this invention include the Bareco Waxes C-7500 and C-8500 of the Petrolite Corporation.

In the process of this invention, the microcrystalline wax can be dispersed in the polyamide in several different ways prior to extrusion of the polyamide in filamentary form. For example, in the typical process wherein a polyamide filament is formed by extrusion of a molten polyamide, the invention provides an improvement which comprises adding to the molten polyamide from about 0.1 to about percent, based on the weight of the polyamide, of a microcrystalline wax having a refractive index greater than 1.5 and less than 1.6 and then dispersing the wax in the molten polyamide before said extrusion. In another embodiment comprising a process wherein a polyamide is prepared by polymerization of polyamide-forming reactants, a filament is formed by extrusion of the polyamide and the polyamide is molten from the completion of the polymerization until after said extrusion, the invention provides an improvement which comprises dispersing in the molten polyamide form about 0.1 to about 5 percent, based on the weight of the polyamide, of a microcrystalline wax having a refractive index greater than 1.5 and less than 1.6. In still another embodiment comprising a process wherein a molten polyamide is prepared by polymerization of polyamide-forming reactants, the molten polyamide is solidified and the resulting solid polyamide is remelted and then extruded in the form of a filament, the invention provides an improvement which comprises dispersing in the molten polyamide from about 0.1 to about 5 percent, based on the weight of the polyamide, of a microcrystalline 'wax having a refractive index greater than 1.5 and less than 1.6.

For best results, the wax and the molten polyamide should be mixed with sufficient thoroughness that the wax is substantially uniformly dispersed throughout the resulting mixture. Such thorough mixing is often most conveniently achieved by mixing the wax with the polyamideforming reactants prior to completion of the polymerization reaction because the reactants are normally agitated during the polymerization reaction and the need for a subsequent additional mixing step is thereby avoided. Substantial filament lubricity improvements are achieved by the use of from about 0.1 to about 5 percent of the wax, based on the weight of the polyamide in which it is dispersed. Superior results are generally obtained by the use of from about 0.25 to about 3 percent of the wax on the same weight basis.

The polyamide filaments of improved lubricity as provided by the process of this invention are highly suitable for many uses. For example, they may be used in a variety of textile applications such as fabrics and woven and tufted articles such as carpet and the like, as well as in reinforcement of elastomeric articles such as pneumatic vehicle tires.

COMPARATIVE EXAMPLE A grams of hexamethylene diammonium adipate and 50 grams of water were charged to a stirred stainless steel high-pressure autoclave which was then purged of air and pressurized to 250 p.s.i.g. with purified nitrogen. The temperature of the reaction mixture was gradually raised to 243 C. during which time steam was withdrawn from the autoclave. Next, the autoclave pressure was gradually lowered to about one atmosphere over a 25-minute period during which the polymer temperature was made to level out at 278 C. At that point, the molten polymer was allowed to equilibrate for 30 minutes. The finished polymer was then extruded from the bottom of the autoclave through a single-orifice spinneret and the resulting monofilament was drawn at a draw ratio of 4.67 to 1. After preconditioning at 72 F. and 35% relative humidity for 24 hours, the lubricity of the drawn monofilament was determined by measuring the fiber-to-fiber frictional force that was present when the fiber rubbed against itself while twisted over itself through two Z turns (720 contact). The frictional force was measured at fiber rubbing speeds of 0.01, 0.05, 0.1, 0.5 and 1.0 meter per minute under a constant load of 2.5 grams. The results of the lubricity tests are set forth in the table.

EXAMPLE I The procedure of Example A was repeated with the exception that 0.5 weight percent (based on the weight of the resulting polymer) of a microcrystalline wax (Bareco7500) having a melting point of 96 C. and a refractive index between 1.528 and 1.530 at 23 C. was mixed with the reaction mixture before polymerization was begun and the resulting monofilament was drawn at a draw ratio of approximately 5 to 1. The drawn monofilament was identical in appearance to that of Example A. The results of the lubricity tests are set forth in the table.

EXAMPLE II The procedure of Example I was repeated with the exception that 2 weight percent of the wax was mixed with the reactants before polymerization was begun and the resulting monofilament was drawn at a draw ratio of 4.79 to l. The drawn monofilament was identical in appearance to that of Example A. The results of the lubricity tests are set forth in the table.

[Fiber-to-fiber frictional force in grams] Fiber rubbing speeds in meters per minute Example:

A. 2.1 2.4 2.5 2.6 2 9 1.- 1.7 1.7 1.9 2.0 2 3 II 0.8 1.0 1.0 1.1 1 1 EXAMPLES III AND IV EXAMPLE V When the procedures of Examples A and I-IV are repeated with the exception that e-caprolactam is substituted for the hexamethylene diammonium adipate and the polymer equilibration period is extended to 90 minutes, the results are similar. That is, the drawn monofilaments containing the microcrystalline wax are identical in appearance to the filament containing no wax and exhibit substantially lower fiber-to-fib-er frictional forces than those of the filament containing no wax under the conditions of the aforedescribed lubricity test.

We claim:

1. In a process wherein a polyamide is prepared by polymerization of polyamide-forming reactants, a fila ment is formed by extrusion of the polyamide and the polyamide is molten from the completion of the polym erization until after said extrusion, the improvement which comprises dispersing in the molten polyamide from about 0.1 to about 5 percent, based on the weight of the polyamide, of a microcrystalline wax having a refractive index greater than 1.5 and less than 1.6.

2. A process as defined in claim 1, in which the wax is dispersed in the molten polyamide by mixing the wax with the polyamide-forming reactants before completion of the polymerization.

3. A process as defined in claim 1, in which the polyamide-forming reactants are selected from the group consisting of (a) substantially equimolar proportions of (1) at least one organic dicarboxylic acid containing from 4 to carbon atoms or a polyamide-forming derivative thereof and (2) at least one organic diamine containing from Q to 20 carbon atoms or a polyamide-forming derivative thereof and (b) at least one aminocarboxylic acid containing from 4 to 20 carbon atoms or a polyamide-forming derivative thereof.

4. A process as defined in claim 1, in which the polyamide-forming reactants are selected from the group consisting of e-aminocaproic acid, e-caprolactam and substantially equimolar proportions of adipic acid and hexamethylene diamine.

5. In a process wherein a molten polyamide is prepared by polymerization of polyamide-forming reactants, the molten polyamide is solidified and the resulting solid polyamide is remelted and then extruded in the form of a filament, the improvement which comprises dispersing in the molten polyamide from about 0.1 to about 5 percent, based on the weight of the polyamide, of a microcrystalline wax having a refractive index greater than 1.5 and less than 1.6.

6. A process as defined in claim 5, in which the wax is dispersed in the molten polyamide by mixing the wax with the polyamide-forming reactants before completion of the polymerization.

7. A process as defined in claim 5, in which the polyamide-forming reactants are selected from the group consisting of (a) substantially equimolar proportions of 1) at least one organic dicarboxylic acid containing from 4 to 20 carbon atoms or a polyamide-forming derivative thereof and (2) at least one organic diamine containing from 2 to 20 carbon atoms or a polyamide-forming derivative thereof and (b) at least one aminocarboxylic acid containing from 4 to 20 carbon atoms or a polyamide-forming derivative thereof.

8. A process as defined in claim 5, in which the polyamide-forming reactants are selected from the group consisting of e-aminocaproic acid, e-caprolactam and substantially equimolar proportions of adipic acid and hexamethylene diamine.

9. In a process wherein a polyamide filament is formed by extrusion of a molten polyamide, the improvement which comprises adding to the molten polyamide from about 0.1 to about 5 percent, based on the weight of the polyamide, of a microcrystalline wax having a refractive index greater than 1.5 and less than 1.6 and then dispersing the wax in the molten polyamide before said extru- 10. A process as defined in claim 9, in which the polyamide is a product of polymerization of polyamide-forming reactants selected from the group consisting of (a) substantially equimolar proportions of (1) at least one organic dicarboxylic acid containing from 4 to 20 carbon atoms or a polyamide-forming derivative thereof and (2) at least one organic diamine containing from 2 to 20 carbon atoms or a polyamide-forming derivative thereof and (b) at least one aminocarboxylic acid containing from 4 to 20 carbon atoms or a polyamide-forming derivative thereof.

11. A process as defined in claim 9, in which the polyamide is a product of polymerization of polyamide-forming reactants selected from the group consisting of eaminocaproic acid, e-caprolactam and substantially equimolar proportions of adipic acid and hexamethylene diamine.

References Cited UNITED STATES PATENTS 3,008,908 11/1961 Voigt 26028 3,262,989 7/ 1966 Brignac 26028 3,378,056 4/1968 Robertson 26028 3,461,092 8/1969 Story 260-28 OTHER REFERENCES Warth: The Chemistry and Technology of Waxes, 2nd edition, Reinhold Pub. Co., 1956, pp. 138, 139.

MORRIS LIEBMAN, Primary Examiner P. R. MICHL, Assistant Examiner US. Cl. X.R. 264--211 

